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Chapter 40 Suggested solutions for Chapter 40 361 Purpose of the problem Reminder of nitrenes as analogues of carbenes after a routine carbene insertion. Suggested solution The diazoester gives the carbene under Cu(I) catalysis, and insertion into the alkene follows its usual course. The only extra is the stereoselectivity: the insertion happens more easily if the two large groups (Ph and CO₂Et) stay as far apart as possible. CO₂Et : CH Ph Ph Conversion of acid derivatives into amines with the loss of the carbonyl group can be done in The product is an antidepressant ways. In Chapter 40 we recommended either the Curtius rearrangement or the Hofmann discovered by A. Burger and (p. 1073). The Hofmann degradation is easier starting with an ester. We convert into W.L. Yost, J. Am. Chem. Soc., amide with ammonia and treat with bromine in basic solution. The N-bromo derivative forms a 1948, 70, 2198. by α-elimination that rearranges to an isocyanate. CO₂Et NH₃ CONH₂ Br₂ Br NaOH Ph Ph Ph N NaOH 0 o N Ph Ph Problem 8 Explain how this highly strained ketone is produced, albeit in very low yield, by these reactions. How would you attempt to make the starting material? 1. (COCI)₂ Me₃Si CO₂H 0 2. 3. Cu(I)Br Purpose of the problem To show that intramolecular carbene insertion is a powerful way to prepare cage compounds. Suggested solution Oxalyl chloride makes the acid chloride (details on p. 296) and diazomethane converts this into the (details on p. 1057). Me₃Si o (COCI)₂ CH₂N₂ COCI N=N Me₃Si acid (acyl) chloride Now the carbene chemistry. Treatment with Cu(I) removes gaseous nitrogen and forms the This very strained ketone was Incredibly, this is able to reach across the molecule and insert into the alkene forming one used in a vain attempt to make tetrahedrane by G. Maier and group, three- and two new four-membered rings in one step. You will not be surprised that the yield in this Angew. Chem., Int. Ed. Engl., 1983, reaction is rather low (about 10%). 22, 990. 0 Cu(I)Br e N